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Autism spectrum disorder (ASD) is a neurodevelopmental disorder estimated to affect up to 1.7% of children in the United States, according to the Centers for Disease Control and Prevention (CDC) (Maenner et al., 2020), and 3% of children age 4 years in the United States (Christensen et al., 2019). Children with ASD have impairments in social and communication interactions and restrictive/repetitive behaviors that affect their functional abilities. ASD is one of the fastest growing pediatric disorders and affects boys four times more often than girls (Maenner et al., 2020). The prevalence of ASD has risen dramatically in recent years, with estimates from 1:150 children in the year 2000 to 1:54 children in 2020 (1:34 boys, 1:144 girls) an increase of 175% since 2000 (Maenner et al., 2020). Autism affects all ethnic and socioeconomic groups; prevalence estimates are approximately identical for children who identify as non-Hispanic white, non-Hispanic black, and Asian/Pacific Islander (18.5, 18.3, and 17.9, respectively) but lower for children who identify as Hispanic (15.4) (Maenner et al., 2020). Co-occurring conditions are common in children with ASD, including sleep disorders and seizures; other developmental or behavioral diagnoses, such as attention deficit-hyperactivity disorder (ADHD), anxiety, and mood disorders; and behavioral disorders, such as food refusal, self-injury, and aggression (Coury, 2010; Hossain et al., 2020). Both fine and gross motor skills may be delayed in preschool-age children with ASD (Lloyd, MacDonald, & Lord, 2013). Children with ASD are more likely to have delays in gross motor skills and coordination compared with children in the general population and may meet DSM-5 criteria (see next paragraph) for developmental coordination disorder (DCD) in addition to ASD (Bhat, 2020; Dewey, Cantell, & Crawford, 2007).
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No one cause has been identified for ASD; however, extensive research is being conducted to identify specific genes linked to the disorder (Yuen et al., 2017). Children who have a sibling with ASD are at a higher risk of also having ASD (Ozonoff et al., 2011; Ronald et al., 2006; Sumi, Taniai, Miyachi, & Tanemura, 2006; Taniai, Nishiyama, Miyahci, Imaeda, & Sumi, 2008). Currently, studies suggest that ASD develops from a combination of genetic and nongenetic, or environmental influences (Estes & McAllister, 2015; Hallmayer et al., 2011; Huquet, Ey, & Bourgeron, 2013; Rosenberg et al., 2009). Researchers are investigating environmental influences that can further increase risk in individuals who are genetically predisposed to ASD. Environmental influences being researched as associated with ASD include paternal age, maternal physical and mental health during pregnancy, birth order, prematurity, complications during delivery, and infection in early infancy (Gardener, Spiegelman, & Buka, 2011; Karimi, Kamali, Mousavi, & Karahmadi, 2017; Petrelli, Pucci, & Bezzi, 2016). It is believed that the combination of genetic and/or environmental factors affect crucial aspects of early ...